1. Field of the Invention
The present invention relates to optical surface mount technology. Optical surface mount circuits are based on optical surface mount technology, that optical, opto-electronic, and electrical devices are mounted on the surface of opto-electronic printed wiring boards. Hereinafter, optical surface mount technology, optical surface mount circuit, opto-electronic printed wiring board, opto-electronic surface mount device are abbreviated as O-SMT, O-SMC, OE-PWB, and OE-SMD, respectively.
2. Related Art Statement
Rapidly increasing production of opto-electronic products raises serious problems in the manufacturing process. For instance, almost all fiber-optic communications have shifted to single mode operation, which has resulted in demand of tremendous man-hours for optical alignments and adhesions. One of the authors first proposed Micro-Optics concept in the early period of optical communication development [T. UCHIDA and I. KITANO: Japan Electronic Eng., p22 (Feb. 1969) and T. UCHIDA and S. SUGIMOTO: 8-1, (Invited), 4th ECOC, 1978, Genoa]. Micro-optic devices require a considerable amount of man-hours despite of their reasonably good performances. Silica wave guide IC [T. MIYASHITA et al.: 18D1-1, IOOC 89 (July, 1989, Kobe)] or HOPS (hybrid Optical Packaging on Si [C.H. HENRY, et al.: IEEE J. Lightwave Tech., vol. 7, No. 10, p1530, Oct. 1989]) and OEIC (Opto-Electronic IC) are under intensive development. The serious problems are in mounting these devices on boards, which requires much troublesome work. These problems have not been significantly investigated to date, while packaging technologies for these devices are being well developed.
In current electronics, on the other hand, SMT (Surface Mount Technology) is widely employed in huge and personal computers, communication equipment and home appliances like TV, on account of its merits of high density component mounting and drastic reduction of man hours for board assembly.
O-SMT (Optical Surface Mount Technology [T. UCHIDA: 8th Micro-Optics Seminar Digest, p1, May 1990, Japan]) is intended to present a possible solution to the above-mentioned problems in opto-electronics.
In the meantime, the inventor has formerly proposed in Japanese patent publication No. 48 5,975 (Japanese Patent No. 1002398) a printed type optical circuit as schematically shown in attached FIGS. 15 and 16. That is, depending on a desired pattern, an optical wave guide 32 is formed in a glass substrate 10 extending from one end surface to the other end surface of the glass substrate 10, and the refractive index of the glass substrate 10 is gradually decreased from the central axis of the optical wave guide 32 to the surrounding portion thereof to obtain a circuited substrate for an optical circuit. Usually, when the refractive index is decreased from the central axis of an optical conductor towards the surrounding portion thereof, a light beam passing through the optical wave guide is enclosed therein to assume an optical pass vibrating meandering around the optical axis of the optical wave guide. However, in the aforementioned circuited substrate, an end surface 35 of the optical wave guide 32 is exposed on the end surface of the glass substrate 10, so that an optical part, that is, opto-electronic device, such as a laser diode, etc., has to be attached to the end surface of the glass substrate 10. Hence, a technique of mounting optical parts which is similar to surface mount technology (SMT) in electric systems is not applicable.
In a usual technique of intimately adhering a prism on the optical wave guide to extract a light beam in the optical wave guide it is very difficult in align of the optical axes. Also, a method of using a diffraction lattice to extract a light beam in the optical wave guide has difficulties in mass-producing the diffraction lattice of such minute structure and positioning thereof. In addition, though a method can be considered of providing a groove which penetrates through the optical wave guide 32 from the front surface 30 to the other front surface 31 of the glass substrate 10 in FIG. 16 and fixing the optical part in the groove, the method has drawbacks in practical use in that the processing steps, processing time and processing cost are increased, and alignment of the optical axes is difficult.